The first thing you notice about the actor, director and producer Danny DeVito is that, as has been exhaustively documented, getting on for a zillion times, he's short (five foot nothing) and round, like a human Teletubby. Albeit a 67-year-old Teletubby, with white wisps of hair around his ears, which he pulls at constantly.

The second thing you notice is how animated and expressive he is. It's not a cartoon version of DeVito's native Italian-American, but it's at the turbo end of vibrant. In the rehearsal space where we meet, he's constantly shrugging, gesturing with his hands, laughing so that his glasses fall off his forehead over his eyes; at one point, he even pulls me into an impromptu dance, more of which mortification anon.

During our conversation, there are points where you can see flashes of characters he's played: the theatrically belligerent Louie De Palma in his early hit sitcom, Taxi; the tragicomic Penguin in Batman Returns; the bumptious menace of Mr Wormwood in Matilda.

He's fast-talking, bright and, as might be expected, imbued with natural comic delivery. In response to a question about younger actors, he muses: "Someone coming up who reminds me of me – you mean like Ashton Kutcher and Brad Pitt?"

DeVito is in London, rehearsing for the Neil Simon play The Sunshine Boys at the Savoy theatre, directed by Thea Sharrock. He and Richard Griffiths play a vaudevillian double act reluctantly reuniting for a television special.

The timing for The Sunshine Boys chimed perfectly with the filming breaks for DeVito's TV show, It's Always Sunny in Philadelphia. It's also DeVito's first time in a West End production. "That's right," he says. "It's something that I always thought about doing. People would say to me, 'Why don't you do Broadway?' and my big joke was, nah, the dressing rooms are too small." He laughs: "Which certainly goes for the Savoy. But no, it's a gorgeous theatre."

DeVito says he was at the Savoy almost three decades ago to see a production of Michael Frayn's Noises Off with his wife, Rhea Perlman (who played Carla in Cheers). "I just went to revisit and it's so beautiful, a wonderful stage. I'm really looking forward to it."

Saying that, he admits that taking on the role was daunting – his main theatre work was at the start of his career, before he moved to Los Angeles: "So, it was like, yeah, I loved the project, I loved the people involved, but I did think to myself, 'Are you out of your mind?'"

He certainly cannot be doing it for the money. Since leaving the American Academy of Dramatic Arts in New York in 1966, DeVito has played scores of film and TV roles, from his career-forging turn in Taxi to One Flew Over the Cuckoo's Nest, LA Confidential and Twins. He's also directed films such as Throw Momma From the Train, The War of the Roses, and Hoffa, while being a hugely successful producer, through his company, Jersey Films, of the likes of Pulp Fiction, Erin Brockovich, Matilda, Garden State and Get Shorty.

Now there is the prospect of Twins 2, which DeVito confirms they are discussing with the former governor of California, Arnold Schwarzenegger. This time, Eddie Murphy is down to play their unlikely long-lost sibling. "Triplets!" cries DeVito. "I'm very excited. I was depressed when Arnie became governor for all those years. It cost me a lot of money in more ways than one, believe me. "His face grows deadpan. "He's a Republican and he's a governor – who needed that? "

Producing-wise, DeVito proved he had good instincts when he bought Quentin Tarantino's script for Pulp Fiction sight unseen. "I hadn't seen Quentin direct or act. I hadn't even seen Reservoir Dogs when I bought his next project, which wasn't even written. It was just about him. I liked the way he was talking about it. The guy was just so cool. It seemed simple to me. It was like, when friends of mine said, 'You're going to make a movie called what – Erin Brockovich? What the fuck is that? Nobody is going to see that movie!' I said, 'It's the woman's name, what are you going to do – change it?'"

DeVito is starting to strike me as a personality who needs to have lots of things going on – is he someone who gets bored easily? He looks surprised. "I don't think I've been bored ever. I've always been working on two or three things at a time; whether it was in the early days, or whatever, I was always working on something."

Born into a family of second-generation Italian-Americans, DeVito loved movies but never dreamed that he would end up working in them. In a tough neighbourhood in New Jersey, his father ran various businesses, including a sweetshop and a drycleaning firm.

"My parents worked their tails off, but we weren't the poorest people in town. Some people I went to school with, you could tell they were dirt poor." Drugs were all around. "What we were doing in those days were stolen pharmaceuticals," says DeVito. "Though you could be tempted with heroin, I wasn't. And it was mainly heroin then, there wasn't crack or anything when I was a kid. You went straight to skin-popping and mainlining."

Around that time, he lost a couple of people to drugs. "One of my good friends wound up dying in prison. And this wasn't an uncommon thing. It's like a neighbourhood you could have in London or anywhere in the world – anywhere where there's a concentrated amount of easy stuff to get into."

At 14, DeVito persuaded his father to send him to a Catholic boarding school to keep him out of trouble. What does he think would have happened to him had he stuck around? "I don't know, but I always had the feeling that I would be OK." For a boy of 14, he sounds unusually mature, though DeVito puts this down to his parents' influence.

"They were older than most of my friends' parents, which could be funny sometimes. My mother would take me to school and my friends would say, 'Your grandmother's so nice!' I'd come home and I'd say, 'Ma, this is weird.' And she said [adopts raspy voice], 'Oh well, maybe I'd better dye my hair.' And she did – she dyed it. My sister was a hairdresser, so it was easy for her."

Before he went into acting, DeVito trained as a hairdresser, working alongside his sister. I tell him I can see him working as a hair stylist and really enjoying it. "I did enjoy it, I loved it," he beams. "I can joke about the fact that I was thrust into a bevy of beauties every day and I was one of the straight ones." He grins mock-wolfishly. "But kidding aside, I seriously enjoyed it."

DeVito grew up very close to his two older sisters, who he admiringly describes as "really tough broads". That's a background with a lot of strong female company. Is that why he comes across as woman-friendly now? "I am very friendly with women! Seriously. Not only in a sexual way, which I enjoy. I feel comfortable around them. They were always in my house. My sisters, their girlfriends. I felt like I could sit down and talk to a woman."

And of course there is Perlman. They've been married since 1982, with two daughters and a son. "Yeah, Rhea and I have been together for like a hundred years! Seriously, it's getting on for 40 years now. We didn't get married right away, we lived together, and it was back and forth, in and out, on and off." Are they soulmates? "Oh yeah, that kind of thing, good friends, best friends, we talk to each other every day, we Skype, all of it."

Is Hollywood unfair to women? "I don't think it's only Hollywood, I think it's just generally speaking. Most men somewhere in their psyche are still dragging women around by their hair. It's terrible. I have two daughters, but even before my kids were born I always thought that it was terrible."

In his opinion, feminism has made some men even more reactionary. Does he think that the sexes are too combative? "It's not so much that. I just don't think equality is there at all. And it's not only women. It's inequality for young people, old people, women, minorities – there's no balance. We're seeing that in the world. People feeling that there's an incredible lack of genuine fairness.

"Don't get me wrong, I'm a capitalist, but if I know that my money's into something that I don't want it to be in, then I take it out immediately". These days, DeVito mainly likes to invest in green concerns. "I don't want to propagate more smog in the air, I don't want to deplete the rainforests, I don't want to do anything like that."

So far as his fame is concerned, DeVito wears it lightly, seeming to view it almost as an international welcome mat. "Wherever I am, it's a really good feeling to have that connection to people. I love to go out to talk to people and be with folks. I don't shy away from it." What about the media – did he take any notice of the UK phone-hacking scandal? DeVito grins. "You mean, Rupert? And what's her name, Rebekah? Is she out yet? Did they put an ankle bracelet on her?" He shakes his head. "I think it's good when it's fun. It's horrifying when it's tapping a girl's phone who's missing, who winds up dead. That's bad news. I think it's OK if you're, like, chasing the paparazzi out of your yard. That's all right. I did a bit of that, like at the beach and stuff. I usually say, 'Bring it on, take the pictures, whatever you want!' And everybody's fine. I think the bad thing is when you don't know when to stop. I don't think people would balk at a couple of shots. I think when you're chasing people with their kids, and frightening them, it's no good. You've really got to be a lowlife to do that."

As for his height, far from being a disadvantage among Hollywood's beautiful people, DeVito feels it helped him stand out. "Because I wasn't so average. Early on, when I'd go in for a part, people would go, 'Oh'. [Interested stare.] Later, when they rewind that meeting, it would be, 'We've seen 20 actors for the role of the servant in The Merry Wives of Windsor, but wait a minute, we've done this already with this guy, so let's try this Danny guy.' I got two Shakespeare parts like that."

DeVito says that being short only felt like a disadvantage as a teenager. "But then I learned how to dance real good. I had to, because I couldn't slow dance." He gestures towards his frame, then glances over. "How tall are you?"

Um, I say, about 5ft 10in. DeVito makes me get up and go to the other end of the room, as if in an acting workshop. "So you're standing there, on your own, and I come over and I'm like, 'Hey, do you want to slow dance to this song?' But it's like, 'No.' [DeVito slumps, downcast.] So what am I going to do?"

While I stand pathetically, Britishly motionless, DeVito grabs my hands and starts whirling around like a dervish. I can't claim that it's reminiscent of the John Travolta/Uma Thurman dance sequence in Pulp Fiction (not with me letting the side down), but it has to be said that DeVito is pretty nifty on his feet. Afterwards, he holds out his hands in a "how about it?" gesture: "You either say no or I get real lucky!"

All of this makes me recall that, in his early days, DeVito shared a bachelor flat with Michael Douglas: "Yeah, but we don't have a height problem," he says drily. "You know, Michael never had any problem with having Danny around. He always says I'm a babe magnet, but I don't know, I think it's the other way around."

Indeed, the fact that he's not conventional leading man material seems far from a touchy subject for DeVito. "It all worked out for me," he says easily. "But acting is like any other business if you've got it in your heart that you want to write stories, or paint paintings, or build bridges, if you want to do anything. Once you've been bitten by that bug, it's your passion and you have to follow it. That's true whether you're tall, short, black, white, green, yellow."

Don't a lot of people get ground down or stifled? "Well, yeah," says DeVito. "Because we're in a world where people have certain prejudices against folks. Whether its religious, age, gender, whatever it is." His own response is to "be Zen about it". "If something good happens to me, I embrace it and let it go. If something bad happens to me, I embrace it and let it go. You have to. It's like something the Dalai Lama once said – that whole philosophy of going into the mouth of the dragon – facing who you are. Most of us are insecure and the other portion of the world are assholes." He shrugs expansively. "So, you can be insecure – so long as you're not an asshole!"

DeVito has been working in Hollywood for so long – does he feel he could afford to relax, call the shots a bit more? "Oh no, you're always in the jungle. That's the way it's gotta be. It costs them a couple of billion dollars just to open up their doors, just to turn the key. So they have to go for the gold. They invest lots of dough, and make these big tempo movies, and then the Pulp Fictions and the Garden States, the smaller movies, can happen.

"You never know what's going to happen," he says. "You just throw the dice and you get lucky. And I surround myself with smart folks – usually young smart folks. It's good to be thought of in a good light, to have a little bit of clout, but you can't carry the ball all by yourself. You need a team. It's like what I'm doing here, it's with a team. I take my hat off to people such as Jackie Mason, who can face the West End in a one-man show. But all I'm thinking is, thank God for Richard Griffiths – I want my peeps around me!"

As if summoned, a small crowd of people, including Griffiths, is starting to gather outside in the corridor. A signal that our time is almost up. I ask DeVito: if I were to talk to you after The Sunshine Boys run, what do you imagine you'd say to me? "That I had a great time. That I knew it was going to be over before it started. Eight shows a week, I want to savour every moment of it." No days off then? "What did you think I was going to do – half of them? Oh no. If you want to learn, you've got to put in the time."

Although it's a comedy, The Sunshine Boys partly reflects on ageing and mortality. Are these things DeVito thinks about? 'Well, you know, I've got a father-in-law who's 93, Rhea's dad, he's not in the greatest shape. That's all going to happen to you, you've got to think about that stuff."

Then there is his friend Michael Douglas, who had throat cancer? "Exactly. Thank goodness he got better, all well and happy." DeVito taps the table, touch-wood style. "My way of seeing it is that so long as you're walking and talking, and you can do things like come to London, and get on stage with Richard Griffiths, and enjoy yourself, it's all good. I've got three great kids, Rhea is going to come to visit me here once I learn my lines – life is good."

He considers himself a lucky man? "Yeah, very fortunate." Is it about making your own luck? "I don't think you can really think like that," he says. "The way I see it, what you've got to do is think of now, this moment. If you're analysing the past, or anticipating too far into the future, you don't really concentrate on what you're doing in this moment, and that's the most important thing. Right now!" DeVito leans forward and taps the table lightly. "Right now is the most important moment in your entire life. It really is! And its not because you're talking to me."